THREE DIMENSIONAL RECONSTRUCTIONS OF THE NEURAL TERMINALS ON THE GUINEA PIG OUTER HAIR CELLS

Abstract

The three-dimensional reconstruction of the neural pole at the base of the hair cells is essential to evaluate the transduction mechanism of mechanoacoustic stimuli into electro-neural events.
To reconstruct the entire arrangements of the nerve endings on outer hair cells (OHC), the serial thick sectioning technique was employed, and the specimens were observed under a high-voltage electron microscope (HVEM) with an accelerating voltage of 1, 000 kV.
The total number of the nerve endings per cell varied from 9 to 24 in OHC₁ and 12 to 17 in OHC₂. Both OHC₁ and OHC₂ were innervated by efferent and afferent endings nerve terminals. Only eight OHC₁ out of 16 (50%) possessed predominant number of afferent endings, whereas 100% of the OHC₂ had such neural arrangement.
The total number of OHC₁ efferent endings was 120 and afferent endings was 127, indicating that OHC₁ in the third cochlear turn were innervated by nearly equal numbers of two types of endings. In the OHC₂, however, the total number of efferent endings was 37 and that of afferent endings was 56 in seven cells, showing an average ratio of approximately 5 to 8.